Return-Path: Sender: "Marvin Kaye" To: lml@lancaironline.net Date: Tue, 21 Dec 2004 18:06:28 -0500 Message-ID: X-Original-Return-Path: Received: from imo-m20.mx.aol.com ([64.12.137.1] verified) by logan.com (CommuniGate Pro SMTP 4.2.5) with ESMTP id 575886 for lml@lancaironline.net; Tue, 21 Dec 2004 17:49:31 -0500 Received-SPF: pass receiver=logan.com; client-ip=64.12.137.1; envelope-from=Sky2high@aol.com Received: from Sky2high@aol.com by imo-m20.mx.aol.com (mail_out_v37_r3.8.) id q.ce.5e738c1c (4238) for ; Tue, 21 Dec 2004 17:48:59 -0500 (EST) From: Sky2high@aol.com X-Original-Message-ID: X-Original-Date: Tue, 21 Dec 2004 17:48:59 EST Subject: TAS from 3 GPS Ground speeds -- Air Speed Calibration X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1103669339" X-Mailer: 9.0 Security Edition for Windows sub 5000 -------------------------------1103669339 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit I came across this method from _http://williams.best.vwh.net/avform.txt_ (http://williams.best.vwh.net/avform.txt) and I believe it would be usable for Calibration of airspeed indicators if you have a good GPS: (http://williams.best.vwh.net/3gs) TAS and windspeed from three (GPS) groundspeeds. Determine your groundspeed on three headings that differ by 120 degrees (eg 40, 160 and 280 degrees), call these v1, v2 and v3 Let vms = (v1^2 + v2^2 + v3^2)/3 a1= v1^2/vms -1 a2= v2^2/vms -1 a3= v3^2/vms -1 mu= (a1^2 + a2^2 + a3^2)/6 Let bp and bm be the roots of the quadratic b^2 -b + mu =0 ie: bp= 1/2 +sqrt(1/4-mu) bm= mu/bp The TAS and windspeed are then given by sqrt(vms*bp) and sqrt(vms*bm) provided that the TAS exceeds the windspeed. If this is not the case, the roots are exchanged. This is a handy way to check your TAS (and the calibration of your airspeed indicator) using your GPS groundspeed, even though the wind is unknown. Scott Krueger AKA Grayhawk N92EX IO320 Aurora, IL (KARR) . -------------------------------1103669339 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable

I came across this method from http://williams.best.vwh.ne= t/avform.txt and=20 I believe it would be usable for Calibration of airspeed indicators if you h= ave=20 a good GPS:

TAS and windspeed from three (= GPS)=20 groundspeeds.

Determine your ground= speed=20 on three headings that differ by 120 degrees (eg 40, 160 and 280 degrees), c= all=20 these v1, v2 and v3

Let

=
 &=
nbsp;   vms =3D (v1^2 + v2^2 + v3^2)/3     a1=3D v1^2/vms -1
&nbs=
p;    a2=3D v2^2/vms -1

 &nb=
sp;   a3=3D v3^2/vms -1

  &n=
bsp;  mu=3D (a1^2 + a2^2 + a3^2)/6

Let bp and bm be the=20= roots=20 of the quadratic b^2 -b + mu =3D0 ie:

   =
  bp=3D 1/2 +sqrt(1/4-mu)

  &nbs=
p;  bm=3D mu/bp

The TAS and windspeed= are=20 then given by sqrt(vms*bp) and sqrt(vms*bm) provided that the TAS exceeds th= e=20 windspeed. If this is not the case, the roots are exchanged. This is a handy= way=20 to check your TAS (and the calibration of your airspeed indicator) using you= r=20 GPS groundspeed, even though the wind is unknown.

S= cott Krueger=20 AKA Grayhawk
N92EX IO320 Aurora, IL=20 (KARR)

.

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